Inkjet printers can accomplish low-cost and high-quality color printed material easily. As such, such printers are widely used not only in offices, but also by general users due to the increasing popularity of personal computers and imaging devices such as digital cameras. For example, the increased use of digital cameras has largely driven the market for inkjet photo printers.
Generally, in an inkjet printer, a moving part referred to as a carriage, for example, integrally comprising ink cartridges and print heads moves back and forth on a print medium in a direction crossing a direction to convey the medium, and nozzles of the print head jet (eject) liquid ink drops to form minute ink dots on the print medium. In this manner, pre-determined characters or images can be rendered on the print medium to create desired printed material. A typical carriage includes ink cartridges for four colors including black (and yellow, magenta, cyan) and a print head for each of the colors, so that not only monochrome print, but also full color print in combination of the respective colors can be easily performed (further, print in six colors including the colors light cyan and light magenta, seven colors, and eight colors are practically implemented).
A particular type of inkjet printer is a multi-level inkjet printer that uses a multi-level inkjet head wherein its individual jets have the ability to fire a plurality of drop sizes. For example, such inkjets may emit a small, medium, or large drop (or no drop at all). Some multi-level inkjet heads perform halftoning utilizing a set of probability density functions, similar to TRCs (Tone Reproduction Curves), which control the probability that a drop of a certain size is jetting from a given jet; there is a separate probability density function for each possible drop size of the jets. Due to implementation constraints those probability density functions are quantized to a certain bit depth, similar to the quantization of TRCs. Since there are several probability density functions used in the halftoner quantization errors accrue quickly and degrade performance more quickly than bi-level systems that only have one controlling function (e.g., a TRC).